Land-based pollutants threaten coastal aquifers, highlighting the need to protect groundwater and nearshore marine ecosystems. While aquifer heterogeneity has been recognized as a significant factor affecting solute behavior, the impact of fractures on land-sourced solute transport in coastal aquifers remains unclear. This study attempted to address this issue through laboratory experiments and discrete fracture matrix (DFM) models. The impact of horizontal fractures on the temporal and spatial characteristics of solute transport, spreading, and discharge under seawater intrusion was analyzed based on variations in fracture position and length. The results show that fractures/low-velocity zones (LVZ) can accelerate/delay solutes, dividing them into different transport modes and enhancing/prolonging their spreading/discharge duration. Changes in fracture position and length also affect its transport acceleration and path deviation abilities, which ultimately determine when solute discharge occurs. The mixing zone and unsaturated zone, in addition to the LVZ, hinder solute transport, reducing the rate and delaying the end of solute discharge. Meanwhile, fractures facilitate solute transport into the saltwater wedge, expanding the solute discharge zone. However, if solutes are initially within the LVZ, their entry into the fracture rely on their distance from the fracture's near-land edge and the size of the fracture's convergence zone.

中文翻译：

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沿海裂隙含水层中陆源溶质运移的室内和数值研究


陆源污染物威胁着沿海含水层，凸显了保护地下水和近岸海洋生态系统的必要性。虽然含水层非均质性被认为是影响溶质行为的重要因素，但裂缝对沿海含水层中陆源溶质运输的影响仍不清楚。本研究试图通过实验室实验和离散断裂矩阵 （DFM） 模型来解决这个问题。根据裂缝位置和长度的变化，分析了水平裂缝对海水侵入下溶质运移、扩散和排放的时空特征的影响。结果表明，裂隙/低速区 （LVZ） 可以加速/延迟溶质，将它们分成不同的传输模式并增强/延长其扩散/放电持续时间。裂缝位置和长度的变化也会影响其输运加速度和路径偏差能力，这最终决定了溶质放电的时间。除了 LVZ 之外，混合区和不饱和区还阻碍了溶质的运输，降低了速率并延迟了溶质排出的结束。同时，裂缝有助于溶质运入盐水楔，扩大溶质排放区。然而，如果溶质最初位于 LVZ 内，则它们进入裂缝取决于它们与裂缝近陆边缘的距离以及裂缝会聚区的大小。